The invention relates to a control system for the displacement of the specifically lighter liquid components from a self-emptying separator from which at least the specifically heavier liquid component is carried out by means of a paring disk or through a conduit sealingly joined to the drum, in which conduit a throttling means is installed. This displacement takes place before the ejection apertures in the periphery of the drum are opened for the ejection of the solids separated from the liquid mixture. In this manner the loss of the specifically lighter useful liquid that is still in the drum is avoided.
For the operation of the necessary valves and the control of the required waiting periods, control systems are used almost always. Such a control system is known from German Pat. No. 1,142,795, for example.
In clarifying separators which centrifugally separate only the solid impurities from liquids consisting of one or more phases, without at the same time separating mixtures of liquids into their components, the displacement of the liquid filling the central portion of the drum is relatively simple. Drums of this kind have only one liquid outlet. After the solids chamber is filled and it is desired to empty the drum completely, first the raw liquid feed valve is closed and then the inlet is changed over to a specifically heavier displacement liquid. This valve is kept open by the control system until the useful liquid has been displaced inwardly out of the drum. The necessary amount of displacement liquid is approximately equal to the capacity of the drum minus the volume of the solids chamber.
If the clarified liquid is carried away by a paring disk or a conduit hermetically joined to the drum, a valve in this conduit must be closed before the valve is opened which controls the hydraulic fluid which causes the discharge apertures to be opened for the ejection of solids. This prevents losses due to the reverse flow of useful liquid into the drum during the emptying process. After the drum has been emptied, all valves must be restored to their original state in reverse order.
In centrifugal separators which, in addition to removing specifically heavier solids, separate the mixture of liquids into its components, the displacement of the specifically lighter liquid components constitutes a problem. Also, such displacement is involved only when the specifically lighter liquid is the useful component. The raw liquids involved include, for example, fishpresswater, or oils contaminated with solids and water. Centrifugal separating drums have two liquid discharges for the separated components. Their distance from the axis of rotation is normally so adjusted that the separation zone is located within the ascending passages of the plate stack. To displace the specifically lighter liquid components out of the drum, the separation zone must be shifted to the inner liquid level.
In centrifugal separators having a free discharge for both of the liquid components through regulating disks, the position of the separation zone is determined by the inside diameter of the regulating disks in accordance with the difference in the density of the two components. At a normal throughput, it can be changed only by replacing at least one disk with the separator shut down. If the amount of the specifically heavier component greatly exceeds that of the lighter, a displacement of the separation zone towards the inside can accomplished during operation by increasing the infeed to such an extent that more of the specifically heavier liquid enters the drum per unit of time than can pass out over the regulating disk. For this purpose, however, a considerable increase of the input is necessary because very great flows of liquid can pass out over the regulating disk. Exceeding the rated capacity of the drum to such an extent, however, signifies an appreciable reduction of the clarifying performance, so that a portion of the solids becomes entrained in the flow of liquid. This method fails where a plurality of self-emptying separators are operated in parallel. In the case of central control by a single control apparatus, the greatly exceeded nominal capacity would be simultaneously signaled for all separators, which the pump or the cross section of the main supply line, being set for normal throughput, will not provide. But even in the case of the individual control of the individual separators this can happen when several control apparatus coincidentally signal for the increased capacity. Besides, this method is not practicable in the case of raw liquids in which the specifically heavier component is contained in only small amounts. In such cases it is indeed possible to take specifically heavier liquid from a storage tank or also to mix a specifically heavier foreign liquid, in the quantity required for the shifting of the separation zone, with the raw liquid being fed in, or to feed it separately into the drum. However, the unreliability and disadvantages would be the same as in the case of the increase in the input of raw liquid.
In the case of self-emptying separators in which the separated components are removed by means of paring disks, and self-emptying separators of the hermetic or semihermetic type of construction, the increase of the input is also problematical. In drums of this kind, however, the position of the separation zone can be shifted during operation by varying the back pressure by means of a throttling member in at least one of the two discharge lines.
German Pat. No. 659,724 discloses a cream separator from which the cream and the skim milk are removed by means of a paring disk, and in which a throttling means is installed in each of the two discharge lines. The throttling members serve for the adjustment of the back pressure in order to achieve the depth of immersion of the paring disks that is necessary for froth-free removal, and, in the separation of whole milk, to establish the desired ratio of cream and skim milk, i.e., to set the separation zone at the desired position. After the adjustment has been made the throttling members remain unchanged.